在find in rails中使用lambda

Question

我有一个方法，它执行分页的find调用，比如..

1

coll = paginate(:all, lambda {{:conditions => ['status = ? AND expires < ?', 'a', DateTime.now]}}, :select => Constants::POST_FIELDS,
                   :order => 'posts.ratings DESC', :include => [{:poster => :poster_friends}, :category], :per_page => Constants::LISTINGS_PER_PAGE,
                   :page => page)

当此调用运行时，它只是忽略生成的查询中的条件。

2

如果我在named_scope中尝试它，我得到一个错误，如..

named_scope :featured_all, lambda {{:conditions => ['status = ? AND expires < ?', 'a', DateTime.now], order => 'posts.ratings DESC', :include => [{:poster => :poster_friends},  :category],
            :select => Constants::POST_FIELDS}}

命名作用域错误：

/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/hash/keys.rb:47:in `assert_valid_keys'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/base.rb:2101:in `with_scope'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/named_scope.rb:113:in `__send__'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/named_scope.rb:113:in `with_scope'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/named_scope.rb:174:in `method_missing'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/named_scope.rb:188:in `load_found'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/named_scope.rb:166:in `proxy_found'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/named_scope.rb:109:in `is_a?'
    /usr/lib/ruby/gems/1.8/gems/hirb-0.3.1/lib/hirb/formatter.rb:78:in `determine_output_class'
    /usr/lib/ruby/gems/1.8/gems/hirb-0.3.1/lib/hirb/formatter.rb:48:in `format_output'
    /usr/lib/ruby/gems/1.8/gems/hirb-0.3.1/lib/hirb/view.rb:213:in `render_output'
    /usr/lib/ruby/gems/1.8/gems/hirb-0.3.1/lib/hirb/view.rb:126:in `view_output'

对于#1，我做错了什么，为什么它忽略了条件？

对于#2，为什么会出现这个错误？另外，如何传递:page和per_page参数来限制named_scope中的查询。

谢谢

Answer 1

您的用例不保证使用named_scope。你可以像下面这样写一个常规的查找器：

coll = paginate(:select     => Constants::POST_FIELDS,
                :conditions => ['status = ? AND expires < ?', 'a', DateTime.now],
                :include    => [{:poster => :poster_friends}, :category],
                :order      => 'posts.ratings DESC',  
                :per_page   => Constants::LISTINGS_PER_PAGE,
                :page => page)

paginate方法等同于all，因此您不必向paginate方法提供:all结果集范围限定符。

时间值是在执行查询时计算的。这不同于named_scope，您必须使用lambda才能达到相同的效果。

如果需要使用named_scope，请执行以下操作：

named_scope :featured_all, lambda {{
                :select     => Constants::POST_FIELDS,
                :conditions => ['status = ? AND expires < ?', 'a', DateTime.now],
                :include    => [{:poster => :poster_friends}, :category],
                :order      => 'posts.ratings DESC'
               }}

现在，您可以按如下方式使用named_scope

Post.feature_all.paginate(:per_page => Constants::LISTINGS_PER_PAGE, 
                          :page => page)

Answer 2

您的命名作用域在订单键之前缺少:。这可能会破坏指定的作用域。否则，它看起来很好。

也就是说，您不需要使用lambda来获取与当前时间相关的记录。您的数据库提供了类似的方法。例如，如果您使用的是MySQL，则可以使用：

named_scope(:featured_all, {
  :conditions => "status = 'a' AND expires < UTC_TIMESTAMP()",
  :order => 'posts.ratings DESC',
  :include => [{:poster => :poster_friends}, :category],
  :select => Constants::POST_FIELDS
})

UTC_TIMESTAMP()是一个特定于MySQL的函数，它以协调时为单位返回当前日期和时间(哪个Rails应该已经存储了您的DateTimes )。